NK cell activity is regulated by a complex mechanism that involves both activating and inhibitory signals. Several distinct NK-specific receptors have been identified that play an important role in the NK cell mediated recognition and killing of HLA Class I deficient target cells. Natural Cytotoxicity Receptors (NCR) refers to a class of activating receptor proteins, and the genes expressing them, that are specifically expressed in NK cells. Examples of NCRs include NKp30, NKp44, and NKp46 (see, e.g., Lanier (2001) Nat Immunol 2:23-27, Pende et al. (1999) J Exp Med. 190:1505-1516, Cantoni et al. (1999) J Exp Med. 189:787-796, Sivori et al (1997) J. Exp. Med. 186:1129-1136, Pessino et al. (1998) J Exp Med. 188(5):953-60; Mandelboim et al. (2001) Nature 409:1055-1060, the entire disclosures of which are herein incorporated by reference). These receptors are members of the Ig super-family, and their cross-linking, induced by specific mAbs, leads to a strong NK cell activation resulting in increased intracellular Ca++ levels, triggering of cytotoxicity, and lymphokine release, and an activation of NK cytotoxicity against many types of target cells.
CD94/NKG2A is an inhibitory receptor found on subsets of natural killer cells (NK cells), Natural Killer T cells (NKT cells) and T cells (α/β and γ/δ). CD94/NKG2A restricts cytokine release and cytotoxic responses of aforementioned lymphocytes towards cells expressing the CD94/NKG2A-ligand HLA-E (see, e.g., WO99/28748). HLA-E has also been found to be secreted in soluble form by certain tumor cells (Derre et al., J Immunol 2006; 177:3100-7) and activated endothelial cells (Coupe) et al., Blood 2007; 109:2806-14). Antibodies that inhibit CD94/NKG2A signalling may increase the cytokine release and cytolytic activity of lymphocytes towards HLA-E positive target cells, such as responses of CD94/NKG2A-positive NK cells responses towards virally infected cells. Therefore, therapeutic antibodies that inhibit CD94/NKG2A but that do not provoke the killing of CD94/NKG2A-expressing cells (i.e. non-depleting antibodies), may induce control of tumor-growth in cancer patients. In addition, anti-NKG2A antibodies have also been suggested for use in treating autoimmune or inflammatory diseases (see, e.g., US20030095965, WO2006070286).
Various antibodies against NKG2A have been described in the art. WO2006070286 and U.S. Pat. No. 8,206,709 (see also WO2008/009545) describe anti-NKG2A antibody Z270, while WO2009/092805 describes humanized anti-NKG2A antibody Z199. Vance et al. (J Exp Med 1999; 190: 1801-12) refers to rat anti-murine NKG2-antibody 20D5 (now commercially available via BD Biosciences Pharmingen, Catalog No. 550518, USA); and U.S. patent application publication 20030095965 describes murine antibody 3S9. Antibody Z270 binds and neutralizes the inhibitory receptor NKG2A without neutralizing the activating receptors NKG2C and NKG2E. Antibody Z199, 20D5 and 3S9 all bind the activating NKG2 family members NKG2C and NKG2E in addition to NKG2A. Antibody Z270 blocks the binding of HLA-E to NKG2A, while antibody Z199 neutralises NKG2A without interfering with the binding of NKG2A to H LA-E.